Because of the progress of technologies, various electronic products have been shown up in the marketplace. It is widely known that the core of an electronic products is a printed circuit board. The normal operation of the electronic element mounted on a printed circuit board is a key factor for allowing an electronic product to function normally. However, signals of different frequencies are present in electronic circuits and systems. When there exists a frequency difference between signals, a mutual interference between electronic circuits and systems will be produced and cause the electronic product unstable or produce an acoustic noise. For some electronic products or video games requiring a high stability, it is not allowable to have an unstable function, noise interference and acoustic noise.
Taking a Play Station II (PS2) which is popular nowadays as an example, the power supply system thereof generally includes a power converting module operating at multiple operation frequencies for providing a predetermined level of output voltage to a joystick of an electronic entertainment machine or a central processing unit of an externally-connected device etc. The conventional power supply system having multiple outputs will implement each power supply as an independent power converting module. However, in order to comply with a trend of miniaturization of an electronic product, it is not quite cost effective if multiple power supplies are respectively implemented as an independent power module. Thus a current method for solving this situation is to put all the individual power converting modules together.
However, even all the individual power converting modules are combined together, a thorny problem is still inevitable. That is, when each power converting module having different operation frequency is combined together, they will interfere with each other and become unstable. Generally, the ground plane of the printed circuit board utilizes a piece of copper foil in its entirety to connect the ground pins of the electronic elements in each power converting module, and thus a complete ground plane loop will be formed and noise interference is produced accordingly. Therefore, in order to solve this problem, a method of frequency synchronization has been put into practiced presently. The so-called frequency synchronization is to conform the operation frequencies of multiple outputs to each other. Such frequency synchronization method has two advantages. The first one is that the operation frequency of the multiple outputs will not be different with each other once the frequency synchronization is accomplished. Because a power converting module operating at a different frequency will interfere the output of other power converting module, no matter how many power converting modules will be, operation frequency difference will not be produced after synchronization, so that the outputs of other power converting modules will not interfere with each other, and the stability of other power converting modules will not be influenced. The second one is that because the operation frequency has been synchronized and the frequency difference is obviated, acoustic noise will not be produced. Generally, the “buzz” sound produced by the machine is exactly ascribed to this situation. Thus, the method for solving the acoustic noise is to synchronize the operation frequency.
However, if the operation frequency of each power converting module is synchronized, all the operation frequencies will be forced to accommodate to the highest one. However, some power converting modules do not need to have such a high frequency in use. Furthermore, the higher the frequency, the greater the noise interference, and the higher cost of the electronic element will be. Thus, the synchronization of operation frequency will not only cause the application to lose its flexibility but result in a cost waste.
To sum up, no matter the operation frequency of each power converting module is synchronous or asynchronous, three problems will be brought about:
1. If the operation frequencies of multiple outputs are different, the power converting modules will interfere with each other and become unstable.
2. If the operation frequencies of multiple outputs are asynchronous, the power converting module will produce acoustic noise owing to the frequency difference.
3. If the operation frequencies of multiple outputs are synchronous, the operation frequency of all power converting modules will be forced to accommodate to the highest one. Also, under this condition, the application thereof will be inflexible, but and the cost will become higher when the frequency is higher, leading to a cost waste.
Consequently, how to solve the problems described above is the main purpose of the present invention.